Process for preparing 6-chloro-2-nitro-1-methylbenzene-4-sulphonic acid



Patented May 20, 1930' UNITED STATES PATENT OFFICE IRANZ HEN'LE AND BABTHOLOMAUS 'VOSSEN, OE HQCHST-ON-THE-MAIN, GERMANY,

ASSIGNORS '10 GENERAL ANILINE WORKS, INC., 0]! NEW YORK, N. Y., A CORPORA- TION PROCESS FOR PREPARING 6-CHLORO-2-NI'1RO-1-METHYLBENZENE-I-SULPHONIQ ACID 1T0 Drawing. Application filed August 24, 1925, Serial No. 52,216, and in Germany September 1, 1924.

acid containing sulfuric acid anhydride.

The reaction product thus obtainable consists almost completely of 6-chloro-2-nitro-1-- methylbenzene-4-sulphonic acid and contains only a small quantity of an easily separable by-product.

We have furthermore found that one may use in our process as starting material a mixture of 6-chloro-2-nitro-1-methylbenzene nd 4-chloro-2-nitro-1-methylbenzene as it is or instance industrially produced by chlorinating Q-nitro-l-methylbenzene. We have found that the sulfonation of the 6-chlo1o-2-nitro-1- methylbenzene occurs more easily than that of 4-chloro-2-nitro-l-methylbenzene and that it is possible to carry out the. sulfonation process under such conditions that a sulfonation of the 6-chl0ro-2-nitro-1-methylbenzene is effected whereas the l-chloro-2-nitro-1-methylbenzene remains. unaltered.

The above mentioned fact ofiers at the same time a new method of separating the 6-chloro- Q-nitro-l-meth lbenzene from the 4-chloro-2- nitro-l-methyl enzene, which separation could hitherto be effected only by fractional distillation.

It is particularly advantageousto subject to sulfonation the eutectic mixture of 6- chloro-2-nitro-1-methylbenzene and l-chloro- 2-nitro-l-methylbenzene which is produced during the fractional distillation and can not be further separated by fractionation; by I this operation the 4-chl0ro-2-nitro-1 methylbenzene is isolated almost completely in a technically pure state, whereas the 6-chloro- 2-nitro-1-methylbenzene is converted into the 6-chloro -2 nitro 1 methylbenzene 4 sulphonic acid. v

A further object of our present invention is the particular method of separating the sulfonated portion from the non-sulfonated portion. We have made the observation that it is not at all possible to separate in a satisfactory manner the unaltered 4-chloro-2-nitro-1- methylbenzene from the dissolved 6-chloro-2- because the diluted sulfuric acid causes a great part of the non-sulfonated, oily 4- chloro-2-nitro-1-methylbenzene to be suspended and even dissolved. Furthermore,

when the sodium 6-chlorq 2-nitro-1-methylbenzene-l-sulfonateis directly salted out, the nonsulfonatecl 4-chl0ro-2-nitro-l-methylbenzene is enclosed by the formed crystals, which renders a mechanical separation impracticable.

The separation .of the two substances in question can however be elfected by carrying out the saltmg-out operation in two stages,

namely by first adding only so much common salt that the sodium 6-chloro-2-nitro-1- methylbenzene-4-sulfonate is not yet salted out, whereas the non-sulfonated 4-chloro-2- nitro-l-methylbenzene is thereby practically almost completely removed from its suspension or solution. It is onl after the isolation of the non-sulfonated, oi y 4-chloro-2-nitro l-methylbenzene, which can now be easily effected, that the sodium salt of the 6-chloro-2- nitro-1-methylbenzene-4-sulphonic acid is salted out by a further addition of common salt. Also in this case there is still left 2% of 4-chloro-2-nitro-1-methylbenzene in the separated sodium salt of the 6-chloro-2-nitro- 1-methylbenzene-4-sulphonic acid; this remainder can, if required, be removed very easily by distillation with steam, if the mass is previously rendered slightly alkaline with sodium carbonate. The following example illustrates our invention, the parts being by vweight:

Into 4287 parts of the technical mixture of about equal parts of 6-chloro-2-nitro-1 methylbenzene and 4-chloro-2-nitro-l-methyle benzene are run at 7580 (3., while stirring well 6000 parts of oleum of 20% strength. The mixture-is stirred for another 78 hours be exceeded. The resulting mass is stirred dride at a temperature not substantially for some time and the non-sulfonated, oily above 80 C. 4-chloro-2-nitro-1-methylbenzene is then allowed to separate; it is then separated by draining ofl whereupon to the acid aqueous solution are further added, while stirring, 9000 parts of common salt. After cooling, the isolated sodium salt of the 6'-chloro-2- nitro-l-1nethylbenzene-4-sulphonic acid is filtered by suction.

The yield of 6-chloro-Q-nitro-l-methylbenzenei-sulfonate of sodium thus separated amount to more than of the theory with regard to the original percentage of 6-chloro-2-nitro-1-methylbenzene. The yield of unaltered 4-chloro-2-nitro-l-methylbenzene is almost quantitative with regard to the original percentage of 4-chl0ro-2-nitrol-methylbenzene.

By reducing the 6-chloro-2-nitro-l methylbenzene-4-sul1 )honic acid to (i-chloro-Q-aminol-methylbenzcnei-slllphonic acid by the usual methods almost quantitative yields are obtained. 7

The separating process as above described is independent within wide limits of the quantitative proportion of the two isomerides; except that in case of the proportion of 6- chloro-2-nitro-l-methylbenzene to the 4- chloro-Q-nitro-l-methylbenzene in the mixture to be separated being greater than-that in the foregoing example, the respective quantities of oleum and common salt must be adequately increased.

We claim:

1. The process which comprises treating a mixture of 6-chloro-2-nitro-1-methylbenzene and 4-chloro-2-nitro-l-methylbenzene with sulfuric acid containin sulfuric anhydride at a temperature not su stantially above C., treating the resulting reaction mixture with a quantity of sodium chloride suflicient to precipitate the unsulfonated 4-chloro-2- nitro-1-methylbenzene but insufficient to precipitate the sodium salt of 6-chloro-2-nitro-1- methylbenzen'e-et-sulphonie acid in the presence of water, separating the precipitated 4-chloro-2-tnitro-1-methylbenzene from the solution, and treating the'solution with sodium chloride in quantity suflicient to preci pitate the sodium salt of'6-chloro-2-nitro-1- methylbenzene-4-sulphonic acid.

2. The process which comprises treating 6- chloro-2-nitro-1-methylbenzene with sulfuric acid containing sulfuric acid anhydride at a temperature not substantially above 80 C. and isolating the resulting 6-ch1oro-2-nitro- 1-methylbenzene-4-sulphonic acid by salting it out in the presence of water.

3. The process which comprises treating a mixture of 6-chloro-2-nitro-l-methylbenzcne and 4-chloro-2-nitro-l-methylbenzene with sulfuric acid containing sulfuric acid anhy- In testimony whereof, we aflix our signatures.

DR. FRANZ HnNLE. BAR HoLoMAUs VOSSEN. 

